When a building experiences earthquake vibrations its foundation will
move back and forth with the ground. These vibrations can be quite intense,
creating stresses and deformation throughout the structure making the
upper edges of the building swing from a few mm to many inches dependent
on their height size and mass. This is uniformally applicable for buildings
of all heights, whether single storeyed or multi-storeyed in high-risk
earthquake zones.

A building needs to be slightly flexible and also have components, which
can withstand or counter the stresses caused in various parts of the building
due to horizontal movements caused by earthquakes.

In Mexicoearthquake
it was observed that buildings of different sizes and heights vibrated
with different frequencies. Where these were made next to each other they
created stresses in both the structures and thus weakened each other and
in many cases caused the failure of both the structures.

Bureau Of Indian Standards clearly gives
in its code IS 4326 that a Separation Section
is to be provided between buildings.Separation
Section is defined as "A gap
of specified width between adjacent buildings or parts of the same building,
either left uncovered or covered suitably to permit movement in order
to avoid hammering due to earthquake
". Further it states that " For buildings of
height greater than 40 metres, it will be desirable to carry out model
or dynamic analysis of the structures in order to compute
the drift at each storey, and the gap width between the adjoining
structures shall not be less than the sum of their dynamic deflections
at any level."

Thus it is advised to provide adequate gap
between two buildings greater than the sum of the expected bending of
both the buildings at their top, so that they have enough space to vibrate.

Unfortunately in India building bye-laws
permit construction of adjoining houses without gap. The buildings constructed
on them are in varying heights and levels of floors. At the time of an
earthquake these buildings would vibrate with different frequencies. Since
there is no gap between these buildings they would press into each other
creating additional stresses at the points of contact. Normally the buildings
are designed as an individual, thus no provision is provided for the additional
forces coming from the neighbouring house causing initial weakening and
then complete failure of structural components at contact point in earthquakes
of high intensity and where it lasts for a longer duration.

This situation is further compounded when the slab level of one building
is near the mid level of the walls and columns of the neighbouring building,
the walls and columns are normally not designed for taking this additional
shear force caused by the horizontal force coming from the neighbouring
slab. This causes buckling of the columns and walls at times of excessive
stresses at the mid points (courtesy your neighbouring building) and thus
the collapse of the buildings onto each other starting a chain reaction.
Since one cannot predict how one's neighbour is going to build his house
at the time of design it is better to take other precautions such as maintaining
gap.

In the case of high-rise multi storeyed residential
and commercial complexes expansion joints
are provided when the length of the building exceeds a length specified
by code. This expansion joint is provided for relieving stresses caused
due to expansion or contraction of construction material owing to temperature
changes. At this point the buildings are totally separated and a gap of
1 to 2" is provided which is filled with a flexible material. However
this is causing a major problem ie. the deflection of these independent
buildings during earthquake is much more in high rise buildings than the
expansion joint and since at this point these buildings are separate and
of varying size they would swing and hammer with each other and weaken
the buildings. Structural components around the expansion joint would
be severely damaged and there shall be a chain reaction of forces in the
total structure for which the structure has not been designed.

These cracks can be easily observed by just going around Delhi and Gurgaon
and various cities of Gujarat. The damage caused in the recent earthquake
by the seismic forces in the high rise residential and commercial buildings
at the position of expansion joints is clearly visible and indicates to
the gravity of the situstion.

A major problem as seen in the states adjoining Delhi is that, common
wall construction is allowed and long rows of houses or commercial
buildings are made with common walls without gaps. Here again engineers
designing one's house cannot be aware of the forces due to earthquake
which will come from the neighbouring house, who will be sharing your
external wall or structural frame with his. This system is totally against
the principle of earthquake proof construction and design since this puts
in an unknown factor regarding moments and horizontal forces for which
the walls or building frames are to be designed. Further this is also
against the provision of the I.S Code where a building or structure is
to be separated every 30m for allowing expansion caused due to properties
of building materials.

Thus it is advised that in areas where high intensity earthquakes are
expected the following precautions be taken:

1. Municipal and other housing bodies should insure that a suitable gap
is provided between two adjoining buildings at the time of sanction.

2. Town Planners while cutting plots should also keep this provision
of separation of buildings while deciding their size.

3. Instead of expansion joints proper gap as required due to bending/movement
of the two parts of the building due to earthquake be provided in all
buildings.

4. It should be made compulsory to submit structural design, drawings
along with certificate from structural engineer at the time of sanction
of building plans. These should give details of a) soil condition and
bearing capacity. b) Earthquake zone for which the building has been designed.
C) I.S. Codes used for design.

5. All relaxations in building byelaws generally given at the time of
completion should be incorporated at the time of sanction only in the
new byelaws and no relaxation should be permitted afterwards to ensure
that no changes are made in structural design after sanction.

6. Submission of Structural certificate from the designer to the governing
municipal body after casting of foundations and at each floor level should
be made compulsory. This should state that the reinforcement and R.C.C
casted have been verified and are as per his structural design submitted
to the body at time of sanction.

7. Common wall system between adjoining buildings should be totally
abolished.

To summarise, Building Bye - Laws should be amended keeping
in consideration all the recommendations in I.S. Codes. Also start appreciating
the importance of the role of the Structural Engineer, and hire them separately
independent of the Architect to ensure proper structural design. It's
your life at stake and not any one else's. www.indiaarchitectureinfo.com